In the coming year we hope to pursue four main objectives: (1) To complete our analysis of the time of origin and the pattern of migration of the pyramidal cells of the hippocampus and of the granule cells of the dentate gyrus. (2) To analyze, using the autoradiographic method for tracing connections, the association connections within the rat hippocampus. (3) To further perfect the techniques for growing isolated hippocampal cells in vitro and to use these preparations for the analysis of the rules governing the growth and differentiation of dendrites. (4) To obtain further evidence about the time of arrival of the different classes of afferent fibers to the hippocampus and to more completely validate the hypothesis that the distribution of the synapses upon the dendrites of the hippocampal cells is determined not only by their specific chemoaffinities but also by temporal factors.